Methods for removing impurities from coal including neutralization of a leaching solution

ABSTRACT

A method for removing at least one impurity from coal is provided. The method comprises providing coal having a plurality of impurities and contacting the coal with a first leaching solution. The first leaching solution reacts with at least one of the impurities to produce one or more first products soluble in the first leaching solution. The method further comprises adding a neutralizing composition to the first leaching solution. The neutralizing composition reacts with the first leaching solution to form a precipitate. The method further comprises separating at least a portion of the first leaching solution from the coal and the precipitate and contacting the coal and the precipitate with a second leaching solution. The second leaching solution reacts with at least one of the impurities and the precipitate to form one or more second products and one or more third products, respectively, the second products and the third products being soluble in the second leaching solution. The method further comprises separating at least a portion of the second leaching solution from the coal.

TECHNICAL FIELD

This disclosure generally relates to methods for removing impuritiesfrom coal, and more particularly relates to methods for removingimpurities from coal which include neutralization of a leachingsolution.

BACKGROUND OF THE INVENTION

Clean coal, such as ultra clean coal, may be provided by treatment ofcoal including impurities to remove the impurities. For instance, coalincluding impurities may be treated with a first leaching solution suchas hydrofluoric acid (“HF”) in a first reactor to produce a firstreaction slurry. The first reaction slurry may be transported to afilter (e.g., drum filter) to produce filtered, wet coal. The filtered,wet coal may then be transported to a second reactor for treatment witha second leaching solution such as a nitrate solution to produce asecond reaction slurry. The second reaction slurry may then betransported to a filter for filtering. The resulting ultra clean coalmay then be water washed and transported to a dryer for drying.

Typically, the moles of HF required for the first reaction aresignificantly lower than the moles of HF used. Thus, the unreacted HFremains in the liquid and may even remain in the coal (e.g., in theareas of pre-existing moisture and in etched pores in the coal createdfrom the HF reacting with ash impurities) after the coal is filtered.

HF is known to be extremely toxic and to corrode glass. HF typically hasan occupational exposure level of 2 ppm. The PPO's needed include rubbergloves, face mask or safety glasses, apron, and good ventilation. If HFis inhaled or ingested, the result may be fatal. HF is readily absorbedthrough the skin and skin contact may also be fatal. HF also acts as asystemic poison, causes severe burns, and is a possible mutigen. Inaddition, the reaction with HF may be delayed. Thus, any contact withHF, even if minor, requires immediate medical attention.

SUMMARY OF THE INVENTION

This disclosure provides a method for removing at least one impurityfrom coal. The method comprises providing coal having a plurality ofimpurities and contacting the coal with a first leaching solution. Thefirst leaching solution reacts with at least one of the impurities toproduce one or more first products soluble in the first leachingsolution. The method further comprises adding a neutralizing compositionto the first leaching solution. The neutralizing composition reacts withthe first leaching solution to form a precipitate. The method furthercomprises separating at least a portion of the first leaching solutionfrom the coal and the precipitate and contacting the coal and theprecipitate with a second leaching solution. The second leachingsolution reacts with at least one of the impurities and the precipitateto form one or more second products and one or more third products,respectively, the second products and the third products being solublein the second leaching solution. The method further comprises separatingat least a portion of the second leaching solution from the coal.

The present disclosure also provides another method for removing atleast one impurity from coal. The method comprises providing coal havinga plurality of impurities and contacting the coal with a first leachingsolution. The first leaching solution reacts with at least one of theimpurities to produce one or more first products soluble in the firstleaching solution. The method further comprises separating at least aportion of the first leaching solution from the coal as an unreactedfirst leaching solution. The method further comprises adding aneutralizing composition to the unreacted first leaching solution. Theneutralizing composition reacts with the unreacted first leachingsolution to form a precipitate. The method further comprises separatingat least a portion of the unreacted first leaching solution from theprecipitate and contacting the coal and the precipitate with a secondleaching solution. The second leaching solution reacts with at least oneof the impurities and the precipitate to form one or more secondproducts and one or more third products, respectively, the secondproducts and the third products being soluble in the second leachingsolution. The method further comprises separating at least a portion ofthe second leaching solution from the coal.

Other aspects, features, and advantages of this invention will beapparent from the following detailed description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a method 10 for removing at least one impurity fromcoal in accordance with an embodiment of the present invention.

FIG. 2 illustrates a method 50 for removing at least one impurity fromcoal in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

As summarized above, this disclosure encompasses methods for removing atleast one impurity from coal. Thus, the method of the present disclosuremay be used to produce ultra clean coal. As used herein, the term “ultraclean coal” refers to coal having a reduced ash content (e.g., belowabout 0.2%) and/or a substantially reduced sulfur content such that thecoal may be fed directly into processes such as gas turbine processesand provide advantages such as improved thermal efficiency, for example.As used herein, “ash” refers to both the non-combustible components inthe coal before combustion and the non-combustible byproducts resultingfrom combustion of the coal. Embodiments of the method for removing atleast one impurity from coal are described below and illustrated inFIGS. 1 and 2. It should be understood that any system (e.g., gasturbine systems such as coal fired gas turbine systems, pulverized coalpower plants, and integrated gasification combined cycle systems) mayuse the coal (e.g., ultra clean coal) provided by embodiments of themethods of the present disclosure.

FIG. 1 illustrates an embodiment of the method 10 for removingimpurities from coal of the present disclosure. The method 10 firstprovides coal 12 comprising a plurality of impurities. Embodiments ofmethod 10 may provide coal 12 in the form of anthracite coal, bituminouscoal, subbituminous coal, lignite coal, or combinations thereof.

In some embodiments, the impurities include, but are not limited to,oxides of aluminum, iron, potassium, calcium, sodium, and other metals,minerals, inorganic and organic sulfur compounds, alkalis, ash, orcombinations thereof. In certain embodiments, the impurities may bepresent in the coal 12 in an amount ranging from about 2 wt. % to about50 wt. %. In other embodiments, the impurities may be present in thecoal 12 in an amount ranging from about 3 wt. % to about 8 wt. %. Instill other embodiments, the impurities may be present in the coal 12 inan amount ranging from about 5 wt. % to about 7 wt. %.

TABLE 1 Examples of ranges of chemical composition for fly ash producedfrom different coal types (expressed as percent by weight). ComponentBituminous Subbituminous Lignite SiO₂ 20-60 40-60 15-45 Al₂O₃ 5-35 20-3010-25 Fe₂O₃ 10-40  4-10  4-15 CaO  1-12  5-30 15-40 MgO 0-5 1-6  3-10SO₃ 0-4 0-2  0-10 Na₂O 0-4 0-2 0-6 K₂O 0-3 0-4 0-4 LOI 0-15 0-3 0-5Source: http://www.tfhrc.gov

The method 10 contacts the coal 12 with a first leaching solution 14 ina first reactor 16. At least one of the impurities reacts with the firstleaching solution 14 to produce one or more first products soluble inthe first leaching solution. In certain embodiments, the first leachingsolution 14 may comprise an acid solution. In some embodiments, thefirst leaching solution 14 may include, but is not limited to, firstreactants such as a hydrofluoric acid, a nitric acid, a hydrochloricacid, a hydrofluorosilicic acid, a combination thereof, or other strongacids that dissolve oxides.

An example of a reaction of the first leaching solution 14 with at leastone impurity is given below in Formula (I):

SiO₂+4HF→SiF₄+2H₂O  (I).

In certain embodiments, the first leaching solution 14 has a firstreactant concentration ranging from about 3 M to about 10 M. In otherembodiments, the first leaching solution 14 has a first reactantconcentration ranging from about 3 M to about 6 M. In still otherembodiments, the first leaching solution 14 has a first reactantconcentration ranging from about 4 M to about 6 M.

In particular embodiments, the weight ratio of first leaching solution14 to coal 12 added to the first reactor 16 ranges from about 10:1 toabout 10:5. Unless otherwise indicated, all ratios are weight to weightratios. In other particular embodiments, the weight ratio of firstleaching solution 14 to coal 12 added to the first reactor 16 rangesfrom about 10:2 to about 10:4. In still other particular embodiments,the weight ratio of first leaching solution 14 to coal 12 added to thefirst reactor 16 ranges from about 10:2.5 to about 10:3.5.

In certain embodiments, the first leaching solution 14 comprises ahydrofluoric acid solution having a hydrofluoric acid concentrationranging from about 3 M to about 10 M. In other embodiments, the firstleaching solution 14 comprises a hydrofluoric acid solution having ahydrofluoric acid concentration ranging from about 3 M to about 6 M. Instill other embodiments, the first leaching solution 14 comprises ahydrofluoric acid solution having a hydrofluoric acid concentrationranging from about 4 M to about 6 M. In particular embodiments, theweight ratio of hydrofluoric acid solution 14 to coal 12 added to thefirst reactor 16 ranges from about 10:1 to about 10:5. In otherparticular embodiments, the weight ratio of hydrofluoric acid solution14 to coal 12 added to the first reactor 16 ranges from about 10:2 toabout 10:4. In still other particular embodiments, the weight ratio ofhydrofluoric acid solution 14 to coal 12 added to the first reactor 16ranges from about 10:2.5 to about 10:3.5.

In particular embodiments, the coal 12 is in contact with the firstleaching solution 14 for about 1 hours to about 10 hours in the firstreactor 16. In other particular embodiments, the coal 12 is in contactwith the first leaching solution 14 for about 3 hours to about 5 hoursin the first reactor 16. In still other particular embodiments, the coal12 is in contact with the first leaching solution 14 for about 4 hoursto about 5 hours in the first reactor 16.

In particular embodiments, the coal 12 is in contact with the firstleaching solution 14 at a temperature ranging from about 70° F. to about200° F. in the first reactor 16. In other particular embodiments, thecoal 12 is in contact with the first leaching solution 14 at atemperature ranging from about 110° F. to about 170° F. in the firstreactor 16. In still other particular embodiments, the coal 12 is incontact with the first leaching solution 14 at a temperature rangingfrom about 140° F. to about 160° F. in the first reactor 16.

In particular embodiments, the coal 12 is in contact with the firstleaching solution 14 at a pressure ranging from about 14 psia to about1000 psia in the first reactor 16. In other particular embodiments, thecoal 12 is in contact with the first leaching solution 14 at a pressureranging from about 14 psia to about 42 psia in the first reactor 16. Instill other particular embodiments, the coal 12 is in contact with thefirst leaching solution 14 at a pressure ranging from about 14 psia toabout 20 psia in the first reactor 16.

In certain embodiments, the one or more first products comprises one ormore fluorides, hydroxyl fluorides, hydroxides, or combinations thereof.In embodiments where the first products comprise one or more fluorides,the fluorides may be selected from silicon fluoride, aluminum fluoride,iron fluoride, calcium fluoride, potassium fluoride, or combinationsthereof.

The method 10 further comprises adding a neutralizing composition 18 tothe first leaching solution 14 such that neutralizing composition reactswith the first leaching solution to form a precipitate. By adding theneutralizing composition 18 to the first leaching solution 14, anyunreacted first reactant (i.e. excess first reactant that has notreacted with at least one of the impurities) in the first leachingsolution is neutralized.

In some embodiments, the neutralizing composition 18 comprises aneutralizing reactant including a calcium hydroxide, sodium hydroxide,any other alkali, or combinations thereof. In certain embodiments, thefirst leaching solution comprises a hydrofluoric acid solution, theneutralizing composition comprises calcium hydroxide, the precipitatecomprises a calcium fluoride, and the one or more third productscomprise calcium ions, nitrate ions, or combinations thereof.

In certain embodiments, the neutralizing composition 18 is added to thefirst leaching solution 14 after the coal 12 has been in contact withthe first leaching solution for about 1 hours to about 10 hours in thefirst reactor 16. In other particular embodiments, the neutralizingcomposition 18 is added to the first leaching solution 14 after the coal12 has been in contact with the first leaching solution for about 3hours to about 5 hours in the first reactor 16. In still otherparticular embodiments, the neutralizing composition 18 is added to thefirst leaching solution 14 after the coal 12 has been in contact withthe first leaching solution for about 4 hours to about 5 hours in thefirst reactor 16.

In certain embodiments, the neutralizing composition 18 has aneutralizing reactant concentration ranging from about 1 M to about 10M. In other embodiments, the neutralizing composition 18 has aneutralizing reactant concentration ranging from about 1 M to about 4 M.In still other embodiments, the neutralizing composition 18 has aneutralizing reactant concentration ranging from about 2 M to about 3 M.

The method 10 further comprises separating at least a portion of thefirst leaching solution 14 from the coal 12 and the precipitate. Byseparating at least a portion of the first leaching solution 14 from thecoal 12, at least a portion of the first products are also separatedfrom the coal because they are soluble in the first leaching solution.Thus, in particular embodiments, substantially all of the first leachingsolution 14 including substantially all of the first products may beseparated from the coal 12 and the precipitate. In the method 10illustrated in FIG. 1, the first leaching solution 14, the coal 12, andthe precipitate, are transported from the first reactor 16 as a slurry20 to a drum filter 22. The drum filter 22 filters the slurry 20 toseparate the coal and the precipitate as wet coal 26 from the firstleaching solution 24.

The wet coal 26 is then fed to a second reactor 30 where the coal 12 andthe precipitate are contacted with a second leaching solution 28. Thesecond leaching solution 28 reacts with at least one of the impuritiesand the precipitate to form one or more second products and one or morethird products, respectively. The second products and the third productsare soluble in the second leaching solution 28. In certain embodiments,the second leaching solution 28 may comprise a nitrate solution.

Examples of reactions of the second leaching solution 28 with at leastone impurity are given below in Formulas (II) and (III):

FeS₂+14Fe(NO₃)₃+8H₂O→2SO₄ ²⁻+16H⁺+15Fe²⁺+42NO³⁻  (II)

SiF₄+2(Al,Fe)(NO₃)₃+2H₂O→SiO_(2(s))+2(Al,Fe)F₂ ⁺+4H⁺+6NO₃ ⁻  (III).

In certain embodiments, the second leaching solution 28 comprises asecond reactant including, but not limited to nitric acid, aluminumnitrate, ferric nitrate, fluoronitrate, other nitrates, hydroxide,hydroxyl fluoride, hydroxynitrate ions thereof, or combinations thereof.In some embodiments of the method, the one or more second productscomprises nitrate ions, sulfate ions, iron ions, hydroxyfluorides,oxides, fluoronitrate, or combinations thereof. In particularembodiments, the one or more third products comprise calcium ions orcombination thereof.

In particular embodiments, the second leaching solution 28 has a secondreactant concentration ranging from about 0.1 M to about 5 M. In otherparticular embodiments, the second leaching solution 28 has a secondreactant concentration ranging from about 0.1 M to about 0.4 M. In stillother particular embodiments, the second leaching solution 28 has asecond reactant concentration ranging from about 0.3 M to about 0.4 M.

In certain embodiments, the weight ratio of second leaching solution 28to wet coal 26 added to the second reactor 30 ranges from about 10:1 toabout 10:5. In other embodiments, the weight ratio of second leachingsolution 28 to wet coal 26 added to the second reactor 30 ranges fromabout 10:2 to about 10:4. In still other embodiments, the weight ratioof second leaching solution 28 to wet coal 26 added to the secondreactant reactor 30 ranges from about 10:2.5 to about 10:3.5.

In particular embodiments, the second leaching solution 28 comprises anitric acid solution having a nitric acid concentration ranging fromabout 0.1 M to about 5 M. In other particular embodiments, the secondleaching solution 28 comprises a nitric acid solution having a nitricacid concentration ranging from about 0.1 M to about 0.4 M. In stillother particular embodiments, the second leaching solution 28 comprisesa nitric acid solution having a nitric acid concentration ranging fromabout 0.2 M to about 0.3 M. In certain embodiments, the weight ratio ofnitric acid solution 28 to wet coal 26 added to the second reactor 30ranges from about 10:1 to about 10:5. In other embodiments, the weightratio of nitric acid solution 28 to wet coal 26 added to the secondreactor 30 ranges from about 10:2 to about 10:4. In still otherembodiments, the weight ratio of nitric acid solution to 28 to wet coal26 added to the second reactor 30 ranges from about 10:2.5 to about10:3.5.

According to certain embodiments of the present disclosure, the secondleaching solution 28 is in contact with the coal and the precipitate forabout 20 hours to about 30 hours in the second reactor 30. In otherparticular embodiments, the second leaching solution 28 is in contactwith the coal and the precipitate for about 22 hours to about 26 hoursin the second reactor 30.

In particular embodiments, the second leaching solution 28 is in contactwith the coal and precipitate at a temperature ranging from about 70° F.to about 190° F. in the second reactor 30. In other particularembodiments, the second leaching solution 28 is in contact with the coaland precipitate at a temperature ranging from about 150° F. to about1.90° F. in the second reactor 30. In still other particularembodiments, the second leaching solution 28 is in contact with the coaland precipitate at a temperature ranging from about 140° F. to about160° F. in the second reactor 30.

In particular embodiments, the second leaching solution 28 is in contactwith the coal and precipitate at a pressure ranging from about 14.4 psiato about 100 psia in the second reactor 30. In other particularembodiments, the second leaching solution 28 is in contact with the coaland precipitate at a pressure ranging from about 14.4 psia to about 43psia in the second reactor 30. In still other particular embodiments,the second leaching solution 28 is in contact with the coal andprecipitate at a pressure ranging from about 14.4 psia to about 28 psiain the second reactor 30.

The method 10 further comprises separating at least a portion of thesecond leaching solution 28 from the coal. By separating at least aportion of the second leaching solution 28 from the coal, at least aportion of the second products and at least a portion of the thirdproducts are also separated from the coal because they are soluble inthe second leaching solution. Thus, in particular embodiments,substantially all of the second leaching solution 28 includingsubstantially all of the second products and substantially all of thethird products may be separated from the coal. In the method 10illustrated in FIG. 1, the second leaching solution 28 and the coal aretransported from the second reactor 30 as a slurry 32 to a drum filter34. The drum filter 34 filters the slurry 32 to separate wet coal 38from the second leaching solution 36.

The method 10 may further comprise washing the wet coal 38 with water ina water wash apparatus 40 to remove any residual reactants or productsfrom the coal. The water-washed coal 42 may be transferred to a coaldryer (not shown) over a conveyer belt (not shown), which will furtheract as a filter to remove water from the coal.

Ash may be present in particular embodiments of the water-washed coal 42in an amount less than about 0.2% by weight. In certain embodiments ofthe method 10, ash is present in the water-washed coal 42 in an amountranging from about 0.01% by weight to about 0.5% by weight. In otherembodiments of the method 10, ash is present in the water-washed coal 42in an amount ranging from about 0.01% by weight to about. 0.2% byweight.

In particular embodiments, the method further comprises agitating thefirst leaching solution in the first reactor, agitating the secondleaching solution in the second reactor, or both.

FIG. 2 illustrates an another embodiment of a method 50 for removingimpurities from coal. Like elements in FIGS. 1 and 2 are numbered withlike numerals.

As illustrated in FIG. 2, the neutralizing composition 18 is added to anunreacted first leaching solution 54 rather than to the first reactor 16as in the method 10 illustrated in FIG. 1. Thus, in this embodiment, thefirst leaching solution 12 and the coal 14 are transported from thefirst reactor 16 as a slurry 52 to the drum filter 22. The drum filter22 fillers the slurry 52 to separate an unreacted first leachingsolution 54 and from wet coal 56. The neutralizing composition 18 isadded to the unreacted first leaching solution 54 and the neutralizingcomposition reacts with the unreacted first leaching solution to form aprecipitate.

At least a portion of the unreacted first leaching solution 54 isseparated by a filter apparatus 58 from the precipitate 60 as aneutralized first leaching solution 62. The precipitate 60 is thencontacted with the second leaching solution 28 in the nitrate reactor,along with the wet coal 56. The second leaching solution 28 reacts withat least one of the impurities and the precipitate 60 to form one ormore second products and one or more third products, respectively. Thesecond products and the third products are soluble in the secondleaching solution 28.

In alternate embodiments (not shown), the methods may be carried out inone reaction chamber in a batch process to avoid using multiplereactors, multiple filters, and conveying equipment (e.g., pumps andconveyer belts) an associated costs and space requirements. In addition,exposure of coal outside of the reactor is reduced, thus h

By adding a neutralizing composition to the first leaching solutioneither in the first reactor or into an unreacted first leaching solutionseparated from the coal and then contacting the produced precipitatewith the second leaching solution, excess unreacted reactant, such ashydrofluoric acid, is reduced or eliminated from the remainder of theprocess and the resulting coal. Thus, the potential for exposure tohazardous chemicals, such as hydrofluoric acid or other acids used, asit is neutralized rather than transported to the second reactor alongwith the coal. In addition, the reactors volumes may be lower and theprocess can be carried out in a continuous manner instead of in a batchor semi-batch process.

it should be apparent that the foregoing relates only to the preferredembodiments of the present application and that numerous changes andmodifications may be made herein by one of ordinary skill in the artwithout departing from the generally spirit and scope of the inventionas defined by the following claims and the equivalents thereof.

1. A method for removing at least one impurity from coal, the methodcomprising: providing coal having a plurality of impurities; contactingthe coal with a first leaching solution, wherein the first leachingsolution reacts with at least one of the impurities to produce one ormore first products soluble in the first leaching solution; adding aneutralizing composition to the first leaching solution, wherein theneutralizing composition reacts with the first leaching solution to forma precipitate; separating at least a portion of the first leachingsolution from the coal and the precipitate; and contacting the coal andthe precipitate with a second leaching solution, wherein the secondleaching solution reacts with at least one of the impurities and theprecipitate to form one or more second products and one or more thirdproducts, respectively, the second products and the third products beingsoluble in the second leaching solution; and separating at least aportion of the second leaching solution from the coal.
 2. The method ofclaim 1, wherein the neutralizing composition comprises calciumhydroxide, sodium hydroxide, or combinations thereof.
 3. The method ofclaim 1, wherein the neutralizing composition has a neutralizingreactant concentration ranging from about 1 M to about 10 M.
 4. Themethod of claim 1, wherein the first leaching solution comprises ahydrofluoric acid solution, the neutralizing composition comprisescalcium hydroxide, the precipitate comprises a calcium fluoride, and theone or more third products comprise calcium ions, nitrate ions, orcombinations thereof.
 5. The method of claim 1, wherein the firstleaching solution comprises a hydrofluoric acid solution, a nitric acidsolution, a hydrochloric acid solution, a hydrofluorosilicic acidsolution, or combinations thereof.
 6. The method of claim 1, wherein thefirst leaching solution comprises a hydrofluoric acid solution having ahydrofluoric acid concentration ranging from about 3 M to about 10 M. 7.The method of claim 1, wherein the neutralizing composition reacts withthe first leaching solution to neutralize substantially all of the firstleaching solution.
 8. The method of claim 1, wherein the second leachingsolution comprises nitric acid, aluminum nitrate, ferric nitrate,fluoronitrate, hydroxide, hydroxyl fluoride, hydroxynitrate, ionsthereof, or combinations thereof.
 9. The method of claim 1, wherein thesecond leaching solution comprises a nitric acid solution having anitric acid concentration ranging from about 0.1 M to about 5 M.
 10. Themethod of claim 1, wherein the method is carried out in a batch reactorchamber.
 11. A method for removing at least one impurity from coal, themethod comprising: providing coal having a plurality of impurities;contacting the coal with a first leaching solution, wherein the firstleaching solution reacts with at least one of the impurities to produceone or more first products soluble in the first leaching solution;separating at least a portion of the first leaching solution from thecoal as an unreacted first leaching solution; adding a neutralizingcomposition to the unreacted first leaching solution, wherein theneutralizing composition reacts with the unreacted first leachingsolution to form a precipitate; separating at least a portion of theunreacted first leaching solution from the precipitate; contacting thecoal and the precipitate with a second leaching solution, wherein thesecond leaching solution reacts with at least one of the impurities andthe precipitate to form one or more second products and one or morethird products, respectively, the second products and the third productsbeing soluble in the second leaching solution; and separating at least aportion of the second leaching solution from the coal.
 12. The method ofclaim 11, wherein the neutralizing composition comprises calciumhydroxide, sodium hydroxide, or combinations thereof.
 13. The method ofclaim 11, wherein the neutralizing composition has a neutralizingreactant concentration ranging from about 1 M to about 10 M.
 14. Themethod of claim 11, wherein the first leaching solution comprise ahydrofluoric acid solution, the neutralizing composition comprisescalcium hydroxide, the precipitate comprises a calcium fluoride, and theone or more third products comprise calcium ions, nitrate ions, orcombinations thereof.
 15. The method of claim 11, wherein the firstleaching solution comprises a hydrofluoric acid solution, a nitric acidsolution, a hydrochloric acid solution, a hydrofluorosilicic acidsolution, or combinations thereof.
 16. The method of claim 11, whereinthe first leaching solution comprises a hydrofluoric acid solutionhaving a hydrofluoric acid concentration ranging from about 3 M to about10 M.
 17. The method of claim 11, wherein the neutralizing compositionreacts with the unreacted first leaching solution to neutralizesubstantially all of the unreacted first leaching solution.
 18. Themethod of claim 11 wherein the second leaching solution comprises nitricacid, aluminum nitrate, ferric nitrate, fluoronitrate, hydroxide,hydroxyl fluoride, hydroxynitrate, ions thereof, or combinationsthereof.
 19. The method of claim 11, wherein the second leachingsolution comprises a nitric acid solution having a nitric acidconcentration ranging from about 0.1 Mto about 5 M.
 20. The method ofclaim 11, wherein the method is carried out in a batch reactor chamber.